Because commercials for cheap plastic toys will make them want to support child labor in underdeveloped countries while simultaneously absorbing BPA and lead into their skin. They will become greedy little candy mongers that demand candy buffets at their birthday parties and become addicted to HFCS and Red 40 which will lead to lifelong obesity and migraines. They will expect not only a Carnival Christmas, but also an Easter basket that overflows onto the table and floor beneath it.

Additionally, they will demand (in the form of tanturms in Wal Mart while only wearing a diaper in 35 degree weather and drinking Mountain Dew from a bottle purchased with foodstamps) the parent buy them light up shoes and character clothing as seen on TV.

This will ultimately lead to them refusing to return their carts to the corral and life of woodshead, swinging (with vigor) threesomes with their in-laws while eating Subway, and their peens not smelling like Irish Spring.

They will never RSVP and never send a thank you note. They will always use Comic Sans and add cat hair to cakes.

This is why the AAP recommends children limit their television/screen time.